This project is designed to study the membrane characteristics and function of the epidermal Langerhans cell (LC). The availability of viable LC suspensions will permit experiments designed to determine the origin of this cell. Of particular interest are studies designed to characterize the LC surface receptors for complement components and to determine if these receptors are of importance in this cell function. Whether LC-lymphocyte interaction and subsequent LC damage involves complement receptors is presently under study. The capacity of LC to secrete products capable of participating in the inflammatory process will be investigated. The "trophic" functions of LC for lymphoid cells will be investigated by using syngeneic cells in vitro; and its role in vivo will be evaluated by assessing its involvement in a variety of skin diseases in which a cell-mediated immunologic mechanism seems to be involved.